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<DIV><FONT face=Arial size=2>You wouldn't want to trickle a good Lithium pack
because you would need to put more than 8.4 volts on it to get any trickle
current. If somehow one cell got partially discharged it would seem that
charge current would flow through both cells and overcharge the one that hadn't
got discharged. However that cell might set at 4.2 while the other cell
comes up. I guess it is time to purposely unbalance a pair of cells and
put them on the charger and see what happens. I will report
back.</FONT></DIV>
<DIV><FONT face=Arial size=2>Jim</FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=tkeithb@comcast.net href="mailto:tkeithb@comcast.net">Keith Black</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=discussion@nsrca.org
href="mailto:discussion@nsrca.org">discussion@nsrca.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, May 07, 2004 6:18 PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Charging concerns/questions
with NMP Lithium Ion batteries</DIV>
<DIV><BR></DIV>
<DIV>
<DIV><FONT face=Arial size=2>Thanks for your reply Jim. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I do like design of the NMP charger and the way
it shows how much current is being feed to the battery. This is clearly an
excellent design feature. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>What I gather from your response is it is
"possible" for a cell to be charged beyond the safe limit if another cell is
either out of balance or defective. Also, I understand your point that one may
be able to spot a bad cell after becoming familiar with the charger.
</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>As it relates to the cells being unbalanced, will
lithium batteries equalized each other via a "trickle" as is the case with
NiCad batteries?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Jim, I really appreciate your always candid
responses and willingness to assist others on the list.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Thanks,</FONT></DIV>
<DIV><FONT face=Arial size=2>Keith</FONT></DIV></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=JOddino@socal.rr.com href="mailto:JOddino@socal.rr.com">JOddino</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=discussion@nsrca.org
href="mailto:discussion@nsrca.org">discussion@nsrca.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, May 07, 2004 10:30
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Charging
concerns/questions with NMP Lithium Ion batteries</DIV>
<DIV><FONT face=Arial size=2></FONT><FONT face=Arial
size=2></FONT><BR></DIV>
<DIV><FONT face=Arial size=2>Hi Kieth,</FONT></DIV>
<DIV><FONT face=Arial size=2>I believe the NMP solves most of the problems
we have all read about. 1) it is the right type of charger for Li-Ions
and is dedicated to that chemistry by limiting the current and the voltage.
2) it is set for two-cell packs and that cannot be changed by the operator
or on its own. 3) it limits the current to less than the 1C rate (for 2000
mAh packs).</FONT></DIV>
<DIV><FONT face=Arial size=2>Probably its best feature vs. the other
chargers is the meter that tells the operator what is going on. After
you use it a few times you will be able to predict the current at the
beginning and during the charge cycle depending on how many
flights you had. If something is wrong, like a cell way out of wack,
it will give you an indication. Of course it tells you when the pack
is charged and if for some reason it was taking too long you would figure it
out. In other words you will learn what is normal proper charge
current vs. time and could spot an unbalanced pack. It cannot assure
you a cell will not be overcharged if the cells are not matched but I
believe you would spot it.</FONT></DIV>
<DIV><FONT face=Arial size=2>I've been using it for over a year and always
charge the packs in the plane. The total charge time is relatively
short so you can monitor it, but I have left them plugged in over
night. </FONT></DIV>
<DIV><FONT face=Arial size=2>I have only seen one pack (a Duralite which was
in a plane I bought) with a slight unbalance. It was a 2S2P
configuration and I don't have much experience with that
configuration. I have never seen a simple 2 cells in series pack
unbalanced.</FONT></DIV>
<DIV><FONT face=Arial size=2>Where you really need to worry about this is in
long strings like those used in electric flight. I talked to Fred
Marks (FMA) about bringing out each node so each cell could be checked and
charged individually if required. He said they plan to do that in the
future.</FONT></DIV>
<DIV><FONT face=Arial size=2>In the mean time, I believe one could stick a
pin through the heat shrink to check the cell balance. I'll try that
today and get back to the list.</FONT></DIV>
<DIV><FONT face=Arial size=2>Regards, Jim</FONT><FONT face=Arial
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